1. That's because many pot-smokers, frequent or not, also smoke cigarettes.

2. As it says, the ONLY prospective clinical study proves that false.

3. And that statement is correct, taken in the right context.
My neighbors would think that I have chronic cough. That's how I get the chronic phlegm, that causes wheezing, out.

(If you hear your neighbor cough, heavily, even a few times, every day, you'll think that his/her's cough is chronic.)